Mounting point for roll cage

Saw this photo from twitter where the owner is installing the roll cage into a strip out HT81S. Something that caught my eye as being highlighted in the twitter post is the rear mounting point at the rear wheel arch.

I not sure whether this roll cage is custom design to the car or being taken from other model and try to fit in HT81S. However I am a bit sceptical that the rear mounting point require securing into the wheel arch and bolt secure from the bottom of the car. Is that a good mounting point ? Does the wheel arch have the strength to hold it ? The metal look pretty thin there.
Anyway, this post is for sharing and if the owner of the twitter see this and could comments, kindly drop me a comments below.

Read more about my previous roll cage post via the link below :-
http://ht81s.blogspot.com/search/label/roll%20cage